<%@ page contentType="image/jpeg"
	import="java.util.*,java.awt.*,java.io.*,java.awt.image.*,javax.imageio.*"
	pageEncoding="utf-8"%>
<%!   
Color getRandColor(int fc,int bc){//给定范围获得随机颜色   
Random random = new Random();   
if(fc>255) fc=255;   
if(bc>255) bc=255;   
int r=fc+random.nextInt(bc-fc);   
int g=fc+random.nextInt(bc-fc);   
int b=fc+random.nextInt(bc-fc);   
return new Color(r,g,b);   
}   
%>
<%   
//设置页面不缓存   
response.setHeader("Pragma","No-cache");   
response.setHeader("Cache-Control","no-cache");   
response.setDateHeader("Expires", 0);   
  
// 在内存中创建图象   
int width=60, height=20;   
BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);   
  
// 获取图形上下文   
Graphics g = image.getGraphics();   
  
//生成随机类   
Random random = new Random();   
  
// 设定背景色   
g.setColor(getRandColor(200,250));   
g.fillRect(0, 0, width, height);   
  
//设定字体   
g.setFont(new Font("Times New Roman",Font.PLAIN,18));   
  
//画边框   
//g.setColor(new Color());   
//g.drawRect(0,0,width-1,height-1);   
  
// 随机产生100条干扰线，使图象中的认证码不易被其它程序探测到   
g.setColor(getRandColor(160,200));   
for (int i=0;i<100;i++)   
{   
int x = random.nextInt(width);   
int y = random.nextInt(height);   
int xl = random.nextInt(12);   
int yl = random.nextInt(12);   
g.drawLine(x,y,x+xl,y+yl);   
}   
  
// 取随机产生的认证码(4位数字)   
String sRand="";   
for (int i=0;i<4;i++){   
String rand=String.valueOf(random.nextInt(10));   
sRand+=rand;   
// 将认证码显示到图象中   
g.setColor(new Color(20+random.nextInt(110),20+random.nextInt(110),20+random.nextInt(110)));// 调用函数出来的颜色相同，可能是因为种子太接近，所以只能直接生成   
g.drawString(rand,13*i+6,16);   
}   
  
// 将认证码存入SESSION   
session.setAttribute("rand",sRand);   
  
// 图象生效   
g.dispose();   
OutputStream output=response.getOutputStream();   
  
// 输出图象到页面   
ImageIO.write(image, "JPEG", response.getOutputStream());   
output.flush();   
out.clear();   
out = pageContext.pushBody();   
  
%>
